The ability to extract a targeted analyte from a fluid sample has proven to be of great assistance in a variety of analytical applications. For instance, the ability to assay the contents of test samples has proven extremely useful in the testing and examination of biological samples, in particular as analytical testing of biological samples often calls for a wide variety of tests and examinations from a starting sample of a very small volume. In general, micropipettes are used for the handling of these small sample volumes.
The formation of micropipette tips to include a variety of chemistries by packing, coating, or embedding a suitable phase in the tip or on the tip walls has led to the development of micropipette solid phase extraction (SPE) techniques including affinity interactions, hydrophobic interaction, hydrophilic interaction, ion exchange, reverse phase, and the like. This, in turn, has led to improved processing of the samples. For instance, proteins and peptides are often found in buffered solutions that can also contain components such as inorganic salts, low molecular weight organics, urea and detergents. Micropipette SPE tips have been successfully used to isolate the targeted polypeptides from such components prior to characterization and thereby improve the detection limits and the sensitivity of the characterizations.
Problems exist with known devices, however. For instance, many phases that are proposed for use with micropipette tips are limited in possible chemistries. In addition, the sorbent media are often very expensive to prepare and can be quite fragile and easily damaged. Moreover, in designing the devices, e.g., the micropipette SPE tips, there is often a necessary trade-off between surface area available for reaction and efficient fluid transport through the device, i.e., in order to increase available reactive surface area, fluid transport is detrimentally effected, and vice versa. Existing SPE media are often packed into micropipette tips via a porous bead or a monolithic stationary phase. Flow through such media is inefficient, however, and a series of successive aspiration steps is usually required to improve removal efficiency of the process. These additional steps add to the time of sample preparation as well as the complexity of the equipment required.
What is needed in the art are improved sorbent media for SPE applications that can address these and other problems in the art.